Roller retainer, direct-acting guide device and roller screw using the roller retainer

ABSTRACT

In a roller retainer assembly, a roller retainer  15  is thinned to retain individual one of plural rollers  7  circulating in a roller circulation path inclusive of linear and curved races and to hold opposite side surfaces of the roller  7  and front and rear surfaces thereof in the roller moving direction. A combination of linear and curve guide portions  16   a  and  16   b  different in inclination angle and a combination of linear and curve guide portion  17   a  and  17   b  different in inclination angle are formed respectively in opposite end surfaces of the roller retainer  15  in a retainer moving direction. In a linear race, the linear guide portions  16   a  and  17   a  come into contact with adjacent roller retainers  15  respectively. In a curved race, the curve guide portions  16   b  and  17   b  come into contact with adjacent roller retainers  15  respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a roller retainer which is used in adirect-acting guide device, a roller screw, or the like, and in which aroller rolling in a circulation path is held so as to berotatable/slidable.

2. Description of the Related Art

A roller screw having rollers interposed between a screw shaft and a nutmember is known. When the screw shaft is rotated relative to the nutmember, the nut member makes reciprocating motion in a direction of theaxis of the screw shaft. The rollers make rolling motion so as to goaround the outer circumference of a screw groove between the screw shaftand the nut member. Thus, the rollers circulate in a roller circulationpath. A helical roller rolling groove is formed in the screw shaft. Theroller circulation path containing a helical load rolling groovecorresponding to the roller rolling groove is formed in the nut member.In the roller screw, the plurality of rollers maybe arranged in theroller circulation path so as to be parallel to one another to keep theaxes of adjacent rollers approximately parallel to each other, or theplurality of rollers may be arranged in the roller circulation path soas to cross one another to intersect the axes of adjacent rollers.

Generally, in the case of a full-roller type roller screw in which onlyrollers are arranged in the roller circulation path, the respectiverollers make no consistent motion so that each of the rollers falls downin a plane containing the axis of the roller and the direction of themovement of the roller to cause skew. Hence, the rollers are preventedfrom circulating while arranged in the roller circulation path. Thoughnot relating to the roller screw, a belt-like ball retainer forrotatably/slidably holding a plurality of balls of a ball screw to makearranged circulation of the balls is known (for example, seeJP-A-11-223258). The ball retainer holds the balls in the form of alinear chain so that front-side and rear-side adjacent balls cancirculate smoothly.

On the other hand, a cage for holding corresponding one of rollersarranged and received in a circulation path of a direct-acting guidedevice is known (see JP-A-60-205013). FIG. 17 shows such cagescirculating in the roller circulation path of the direct-acting guidedevice. A plurality of rollers 1 are cross-arranged in the rollercirculation path 2 so that the axes of adjacent rollers 1 cross eachother. The direction of the rollers 1 is changed two-dimensionally inbetween a linear load passage 2 a and a U-shaped changing-directionpassage 2 b. FIG. 18 is a front view of a cage 3 with a roller 1 whenviewed in the direction of the movement thereof. FIG. 19 is a sectionalview taken along the line A—A in FIG. 18. Because of the crossarrangement of the rollers 1, the roller circulation path 2 is shapedsubstantially like a square in section. The cages 3 rotatably/slidablyhold the rollers 1 in container holes 3 a of the cages 3 individuallyand correspondingly while the outer circumferences 1 a of the rollers 1are exposed partially slightly. The thickness of the cage 3 (the radialthickness of the roller) is set to be approximately equal to that of theroller 1. As shown in the drawings, the shape of the cage 3 viewed fromthe front side in the direction of the movement forms a squareapproximately equal to the sectional shape of the roller circulationpath 2 so that the roller 1 can be guided by the cage 3. As shown inFIG. 17, two end surfaces 3 a and 3 b which form an angle of not smallerthan 90° are formed at two ends of the adjacent cages 3 in the directionof the movement thereof. When the cage 3 is located on the linear loadpassage 2 a, one end surface 3 a is positioned so as to be approximatelyperpendicular to the load passage 2 a. When the cage 3 is located on theU-shaped changing-direction passage 2 b, the other end surface 3 b isdirected to the direction of the radius of the changing-directionpassage 2 b. Thus, the cages 3 with the rollers 1 circulate in theroller circulation path 2 while the end surfaces 3 a and 3 b of adjacentcages 3 press each other.

In the background-art ball retainer holding balls in the form of astraight chain, however, the circulation path of the ball screw draws aspiral. Hence, the ball retainer is twisted so spirally that load isapplied on the ball retainer. There is a risk that the ball retainer maybe broken by the load.

On the other hand, the cages 3 by which the rollers 1 arranged andreceived in the roller circulation path 2 of the direct-acting guidedevice are held individually are adapted to the case where the linearload passage and the U-shaped changing-direction passage are positionedon one plane so that the direction of the rollers 1 is changedtwo-dimensionally. For example, in a circulation path of a roller screw,however, not two-dimensional direction changing but three-dimensionaldirection changing and, accordingly, twisting motion around thedirection of the movement, may be required. In the aforementioned cages3, the circulating cages 3 are not allowed to rotate slightly around theaxes of the rollers 1 respectively so that the cages 3 can hardly makesuch complex motion. This is because the shape of each cage 3 is formedto be approximately equal to the sectional shape of the rollercirculation path 2 and because adjacent cages 3 are in surface contactwith each other at large-area flat end surfaces 3 a and 3 b. Moreover, alubricant can hardly enter in between the cage 3 and a correspondingroller 1 because the circumference of the roller 1 except part of theouter circumference 1 a is covered with the cage 3. Hence, the roller 1cannot be lubricated sufficiently. Moreover, the approximately wholesection of the roller circulation path 2 is covered with the cage 3.There is a problem that a support member for supporting the cage 3 toprevent the cage 3 from dropping down from the slide member when theslide member is removed from the race rail is hardly provided in thecirculation path.

SUMMARY OF THE INVENTION

An object of the present invention has been made to solve the aboveobject, and therefore an object of the invention is to provide a rollerretainer which can circulate smoothly even in a complex kineticcondition such as a three-dimensional changing-direction passage and inwhich lubricating oil can be supplied sufficiently to rollers, and toprovide a direct-acting guide device and a roller screw using suchroller retainers.

The present invention will be described below. Although the referencenumerals in the accompanying drawings are put in parentheses to makeunderstanding of the present invention easy, the present invention isnot limited to the embodiments based on the accompanying drawings.

To solve the problem, the inventor of the present invention provides asystem in which rollers circulating in a circulating path are not heldin the form of a straight chain but are held in roller retainersindividually so that the rollers circulate in a circulation path whilethe rear-side roller retainer presses the front-side roller retainer.Further, because linear portions and curved portions mainly exit in thecirculation path, the inventor considers the shape of each end of theroller retainer in a direction of the movement thereof so that pressingforce is transmitted smoothly either in the linear portions or in thecurved portions. Further, the inventor provides a system in which rollerretainers can circulate while allowed to rotate slightly around the axesof the rollers respectively when the roller retainers circulate whilepressing each other. Accordingly, the roller retainers can be adapted toa three-dimensionally complex circulation path on the assumption thatthe rollers are arranged in the circulation path and the axes ofadjacent rollers are substantially kept parallel to each other.

Specifically, according to a first aspect of the present invention,there is provided a roller retainer assembly having roller retainers(15) for individually and correspondingly retaining a plurality ofrollers (7) circulating in a roller circulation path inclusive of linearand curved races, wherein: each of the roller retainers (15) is madethin to hold opposite side surfaces of the roller (7) and front and rearsurfaces of the roller (7) in a direction of movement of the roller (7);a linear guide portion (16 a, 17 a) and a curve guide portion (16 b, 17b) which are different in inclination angle from each other are formedin opposite end surfaces of the roller retainer (15) in a direction ofmovement of the roller retainer (15); and the linear guide portion (16a, 17 a) of the roller retainer (15) comes into contact with an adjacentroller retainer (15) in the linear race and the curve guide portion (16b, 17 b) of the roller retainer (15) comes into contact with an adjacentroller retainer (15) in the curved race. By the provision of the rollerretainer assembly, the above-mentioned problem is therefore solved. Thethickness of the roller retainer (15) is selected to be not larger than90%, preferably not larger than 60% of the roller diameter.

According to this invention, in either of linear races and curved racesconstituting a circulation race, adjacent roller retainers can presseach other without spoiling the posture of a roller located in the frontside in the direction of the movement of the roller. Hence, rollers canbe aligned so that smooth circulation can be obtained. Further, becausethe roller retainer is made thin, the following effects are obtained.

(1) Adjacent roller retainers can press each other while they areallowed to rotate slightly around the axes of corresponding rollersrespectively. As a result, the roller retainer can be obtained as aroller retainer adapted to a complex circulation path such as athree-dimensional changing-direction passage or a helical load rollingpassage shaped like a screw.

(2) A large space can be secured for reserving lubricating oil in thecirculation path. Hence, the rollers can be lubricated sufficiently.

(3) A drop-down prevention member for supporting the roller retainer canbe provided in the circulation path so that the roller retainer isprevented from dropping down from the nut member, or the like.

According to a second aspect of the invention, there is provided aroller retainer assembly having roller retainers (31) for individuallyand correspondingly retaining a plurality of rollers (7) circulating ina roller circulation path inclusive of linear and curved races, wherein:each of the roller retainers (31) is made thin to hold the opposite sidesurfaces of the roller (7) and either one of front and rear surfaces ofthe roller (7) in a direction of movement of the roller (7); a linearguide portion (32 a) and a curve guide portion (32 b) which aredifferent in inclination angle are formed in one end surface of theroller retainer (31) in a direction of movement of the roller retainer(31); and the linear guide portion (32 a) of the roller retainer (31)comes into contact with an adjacent roller (7) in the linear race andthe curve guide portion (32 b) of the roller retainer (31) comes intocontact with an adjacent roller (7) in the curved race. By the provisionof the roller retainer assembly, the above-mentioned problem istherefore solved.

According to this invention, in addition to the same operation andeffect as those of the aforementioned invention, the roller retainerholds either of front and rear surfaces of a corresponding roller in thedirection of the movement of the roller. Hence, the space occupied byone roller retainer in the circulation path is reduced so that thenumber of rollers can be increased. Hence, the load capacity of adirect-acting guide device or roller screw using such roller retainerscan be increased.

According to a third aspect of the invention, in the first aspect of theinvention, each of the linear guide portion (16 a, 17 a) and the curveguide portion (16 b, 17 b) of the roller retainer (15) is formed to be acurved surface shaped like a circular arc in section so as to come intolinear contact with the adjacent roller retainer (15).

According to this invention, adjacent roller retainers can press eachother while they are securely allowed to rotate slightly around the axesof corresponding rollers respectively.

According to a fourth aspect of the invention, in the second aspect ofthe invention, each of the linear guide portion (32 a) and the curveguide portion (32 b) of the roller retainer (31) is formed to be acurved surface in accordance with an outer circumference of the roller(7).

According to this invention, a roller and a roller retainer which areadjacent to each other can press each other while the roller retainer issecurely allowed to rotate slightly around the axis of a correspondingroller. Moreover, because the roller retainer comes into surface contactwith a roller located in the front side or rear side in the direction ofthe movement of the roller retainer, contact surface pressure can bereduced.

According to a fifth aspect of the invention, in the roller retainerassembly as stated in the first or third aspect, a hinge protrusion (26)is provided at a point of intersection between the linear guide portion(16 a) and the curve guide portion (16 b) in one end surface of theroller retainer (25); and a hinge recess (27) is provided at a point ofintersection between the linear guide portion (17 a) and the curve guideportion (17 b) in the other end surface of the roller retainer (25) sothat the hinge recess (27) engages with the hinge protrusion (27) of anadjacent roller retainer.

According to this invention, the roller retainer is only allowed toswing around a hinge constituted by a combination of the hingeprotrusion and the hinge recess in a plane containing the axis of acorresponding roller and the direction of the movement of the roller.Hence, the roller can be prevented from falling down even in a boundaryshifting from a linear race to a curved race. Hence, smooth circulationof the roller can be ensured.

According to a sixth aspect of the invention, in any one of the first tofifth aspects, drop-down prevention protrusions (20) are formed oneither one of the roller retainer (15) and the opposite side surfaces ofthe roller (7); and drop-down prevention recesses (21) are formed in theother one of the roller retainer and the opposite side surfaces of theroller so that the drop-down prevention protrusions are fitted into thedrop-down prevention recesses.

According to this invention, the roller can be prevented from droppingout from the roller retainer. For example, even in the case where aslide member such as a nut member is removed from the race rail, theroller retainer can prevent the roller from dropping down from the slidemember so that the roller can be prevented from dropping down from theslide member.

According to a seventh aspect of the invention, in any one of first tosixth aspects, a thickness of the roller retainer (15) is selected to benot smaller than 50% of a diameter of the roller. When a tapered rolleris used as each of the rollers, the terminology “roller diameter” usedherein means the smallest roller diameter.

If the thickness of each of the roller retainers is smaller than 50% ofthe roller diameter, the front end of the succeeding roller retainer inthe circulation path enters the gap between the front-side rollerretainer and the roller rolling groove so that adjacent roller retainersoverlap each other. As a result, there is a risk that the circulation ofrollers may stop. When the thickness of each of the roller retainers isnot smaller than 50% of the roller diameter, such adjacent rollerretainers can be prevented from overlapping each other.

Further, according to the invention, there is also provided adirect-acting guide device comprising: a race shaft (41, 51) containinga roller rolling surface (41 a, 51 a); a slide member (42, 52) includinga roller circulation path containing a load rolling surface (42 a, 52 a)corresponding to the roller rolling surface (41 a, 51 a), the slidemember (42, 52) being fitted to the race shaft (41, 51) so as to befreely movable relative to the race shaft (41, 51); a plurality ofrollers (43, 53) arranged and received in the roller circulation path soas to circulate in accordance with movement of the slide member (42, 52)relative to the race shaft (41, 51); and a plurality of roller retainers(15) for holding the plurality of rollers (43, 53) individually andcorrespondingly so that the plurality of rollers (43, 53) arerotatable/slidable, wherein: the plurality of rollers (43, 53) arearranged and received so that the axes of adjacent rollers (43, 53) arekept approximately parallel to each other; each of the roller retainers(15) is made thin to hold opposite side surfaces of corresponding one ofthe rollers (7) and front and rear surfaces of the roller (7) in adirection of movement of the roller (7); a linear guide portion (16 a,17 a) and a curve guide portion (16 b, 17 b) which are different ininclination angle from each other are formed in each of opposite endsurfaces of the roller retainer (15) in a direction of movement of theroller retainer (15); and the linear guide portion (16 a, 17 a) of theroller retainer (15) comes into contact with an adjacent roller retainer(15) in a linear race and the curve guide portion (16 b, 17 b) of theroller retainer (15) comes into contact with an adjacent roller retainer(15) in a curved race.

Further, according to the invention, there is also provided adirect-acting guide device comprising: a race shaft (41, 51) containinga roller rolling surface (41 a, 51 a); a slide member (42, 52) includinga roller circulation path containing a load rolling surface (42 a, 52 a)corresponding to the roller rolling surface (41 a, 51 a), the slidemember (42, 52) being fitted to the race shaft (41, 51) so as to befreely movable relative to the race shaft (41, 51); a plurality ofrollers (43, 53) arranged and received in the roller circulation path soas to circulate in accordance with movement of the slide member (42, 52)relative to the race shaft (41, 51); and a plurality of roller retainers(15) for holding the plurality of rollers (43, 53) individually andcorrespondingly so that the plurality of rollers (43, 53) arerotatable/slidable, wherein: the plurality of rollers (43, 53) arearranged and received so that the axes of adjacent rollers (43, 53) arekept approximately parallel to each other; each of the roller retainers(31) is made thin to hold opposite side surfaces of corresponding one ofthe rollers (7) and either one of front and rear surfaces of the roller(7) in a direction of movement of the roller (7); a linear guide portion(32 a) and a curve guide portion (32 b) which are different ininclination angle are formed in one end surface of the roller retainer(31) in a direction of movement of the roller retainer (31); and thelinear guide portion (32 a) of the roller retainer (31) comes intocontact with an adjacent roller (7) in a linear race and the curve guideportion (32 b) of the roller retainer (31) comes into contact with anadjacent roller (7) in a curved race.

Further, according to the invention, there is also provided a rollerscrew comprising: a race shaft (5) containing a helical roller rollingsurface (5 a); a slide member (6) including a roller circulation path(8) containing a helical load rolling surface (6 a) corresponding to theroller rolling surface (5 a), the slide member (6) being fitted to therace shaft (5) so as to be freely movable relative to the race shaft(5); a plurality of rollers (7) arranged and received in the rollercirculation path (8) so as to circulate in accordance with movement ofthe slide member (6) relative to the race shaft (5); and a plurality ofroller retainers (15) for holding the plurality of rollers (7)individually and correspondingly so that the plurality of rollers (7)are rotatable/slidable, wherein: the plurality of rollers (7) arearranged and received so that axes of adjacent rollers (7) are keptapproximately parallel to each other; each of the roller retainers (15)is made thin to hold opposite side surfaces of corresponding one of therollers (7) and front and rear surfaces of the roller (7) in a directionof movement of the roller (7); a linear guide portion (16 a, 17 a) and acurve guide portion (16 b, 17 b) which are different in inclinationangle from each other are formed in each of opposite end surfaces of theroller retainer (15) in a direction of movement of the roller retainer(15); and the linear guide portion (16 a, 17 a) of the roller retainer(15) comes into contact with an adjacent roller retainer (15) in alinear race and the curve guide portion (16 b, 17 b) of the rollerretainer (15) comes into contact with an adjacent roller retainer (15)in a curved race.

Further, according to the invention, there is also provided a rollerscrew comprising: a race shaft (5) containing a helical roller rollingsurface (5 a); a slide member (6) including a roller circulation path(8) containing a helical load rolling surface (6 a) corresponding to theroller rolling surface (5 a), the slide member (6) being fitted to therace shaft (5) so as to be freely movable relative to the race shaft(5); a plurality of rollers (7) arranged and received in the rollercirculation path (8) so as to circulate in accordance with movement ofthe slide member (6) relative to the race shaft (5); and a plurality ofroller retainers (15) for holding the plurality of rollers (7)individually and correspondingly so that the plurality of rollers (7)are rotatable/slidable, wherein: the plurality of rollers (7) arearranged and received so that axes of adjacent rollers (7) are keptapproximately parallel to each other; each of the roller retainers (31)is made thin to hold opposite side surfaces of corresponding one of therollers (7) and either one of front and rear surfaces of the roller (7)in a direction of movement of the roller (7); a linear guide portion (32a) and a curve guide portion (32 b) which are different in inclinationangle are formed in one end surface of the roller retainer (31) in adirection of movement of the roller retainer (31); and the linear guideportion (32 a) of the roller retainer (31) comes into contact with anadjacent roller (7) in a linear race and the curve guide portion (32 b)of the roller retainer (31) comes into contact with an adjacent roller(7) in a curved race.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a roller screw in which rollerretainers according to a first embodiment of the present invention areincorporated;

FIG. 2 is a perspective view showing a return pipe which is incorporatedin the roller screw;

FIG. 3 is a perspective view showing a screw shaft in the roller screw;

FIG. 4 is a front view showing a combination of a roller retainer and aroller in the first embodiment of the present invention;

FIG. 5 is a side view showing a combination of a roller retainer and aroller in the first embodiment of the present invention;

FIG. 6 is a bottom view showing a combination of a roller retainer and aroller in the first embodiment of the present invention;

FIG. 7 is a view showing roller retainers and rollers which circulate ina roller screw circulation path;

FIG. 8 is a view showing rollers and roller retainers which circulate ina helical load rolling passage;

FIG. 9 is a view showing an example where adjacent roller retainersoverlap each other;

FIG. 10 is a view showing roller retainers arranged in a circulationpath according to a second embodiment of the present invention;

FIG. 11 is a front view showing a combination of a roller retainer and aroller in a third embodiment of the present invention;

FIG. 12 is a side view showing a combination of a roller retainer and aroller in the third embodiment of the present invention;

FIG. 13 is a bottom view showing a combination of a roller retainer anda roller in the third embodiment of the present invention;

FIG. 14A is a plan view showing an example where roller retainers androllers in the third embodiment of the present invention are aligned ina line;

FIG. 14B is a side view showing an example where roller retainers androllers in the third embodiment of the present invention are aligned ina line;

FIG. 14C is a bottom view showing an example where roller retainers androllers in the third embodiment of the present invention are aligned ina line;

FIG. 15 is a view showing a linear guide in which roller retainersaccording to the first embodiment of the present invention areincorporated (partly including a section taken in a directionperpendicular to a guide rail);

FIG. 16 is a view showing a spline in which roller retainers accordingto the first embodiment of the present invention are incorporated;

FIG. 17 is a view showing cages which circulate in a roller circulationpath of a background-art direct-acting guide device;

FIG. 18 is a view showing a background-art combination of a cage and aroller; and

FIG. 19 is a sectional view taken along the line A—A in FIG. 18.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, a description will be given in more detail of preferred embodimentsof the invention with reference to the accompanying drawings.

FIG. 1 shows a roller screw in which roller retainers according to afirst embodiment of the present invention are incorporated. The rollerscrew comprises a screw shaft 5 (race shaft), a nut member 6 (slidemember), and a plurality of rollers 7. The screw shaft 5 has a helicalroller rolling groove 5 a in its outer circumferential surface so thatthe helical roller rolling groove 5 a serves as a roller rollingsurface. The nut member 6 has a roller circulation path formed in itsinner cirumferential surface. The roller circulation path includes ahelical load rolling groove 6 a so that the helical load rolling groove6 a serves as a load rolling surface corresponding to the roller rollinggroove 5 a. The nut member 6 is fitted to the screw shaft 5 so as to berelatively movable. The plurality of rollers 7 are arranged and receivedin the roller circulation path and circulate in accordance with therelative movement of the nut member 6 to the screw shaft 5. Theplurality of rollers 7 are arranged and received in the rollercirculation path so that axes of adjacent rollers 7 are keptsubstantially parallel to each other. In the roller circulation path, aload rolling passage 8 is formed between the roller rolling groove 5 aof the screw shaft 5 and the load rolling groove 6 a of the nut member6. The nut member 6 has a return pipe. The return pipe forms a no-loadreturn passage by which one end of the load rolling passage 8communicates with the other end of the load rolling passage 8.

FIG. 2 shows the return pipe 9. The return pipe 9 has a body portion 9b, and opposite end portions 9 a bent with respect to the body portion 9b. The opposite end portions 9 a are fitted into the load rollingpassage so that a distance of several pitches is left between theopposite end portions 9 a. Incidentally, the return pipe 9 is fixed tothe nut member 6 by a pipe pressing.

FIG. 3 shows the screw shaft 5. The helical roller rolling groove 5 ahaving a predetermined lead is formed in the outer circumferentialsurface of the screw shaft 5. The roller rolling groove 5 a is shapedlike a trapezoid in section. Each of the rollers 7 rolls on a wallsurface 12 a or 12 b of the roller rolling groove 5 a.

As shown in FIG. 1, the nut member 6 is substantially shaped like acylinder. The helical load rolling groove 6 a having a lead equal to thelead of the screw shaft 5 is formed in the inner circumferential surfaceof the nut member 6. The load rolling groove 6 a is also shaped like atrapezoid in section. A protrusion 10 for forming the load rollinggroove 6 a of the nut member 6 is fitted into the roller rolling groove5 a so that the inner diameter of the nut member 6 is made smaller thanthe outer diameter of the screw shaft 5. Each of the rollers 7 rolls ona wall surface 11 a or 11 b of the load rolling groove 6 a. The loadrolling groove 6 a of the nut member 6 may be shifted in the middle way.Hence, up to the shift position, a space for arranging the rollers 7 isformed between the wall surface 12 b of the roller rolling groove 5 aand the wall surface 11 b of the load rolling groove 6 a and, after theshift position, a space for arranging the rollers 7 is formed betweenthe wall surface 12 a of the roller rolling groove 5 a and the wallsurface 11 a of the load rolling groove 6 a. Return pipe fitting holesare formed in the nut member 6 so that the opposite sides of the returnpipe 9 are inserted in the holes respectively. The return pipe fittingholes extend into the load rolling groove 6 a.

As is obvious from FIG. 2, the return pipe 9 has opposite end portions 9a bent by about 90° with respect to the body portion 9 b. That is, thereturn pipe 9 is substantially formed of a double housing type. Asection of the no-load return passage of the return pipe 9 is determinedin accordance with the shape of each roller 7. As shown in FIG. 2, theopposite end portions 9 a are not parallel to each other so that therespective directions of the opposite end portions 9 a make a torsionalangle θ1 (which changes in accordance with the lead angle).

FIGS. 4 to 6 show roller retainers 15 and rollers 7 which areincorporated in the roller screw. FIG. 4 is a view (front view) in adirection perpendicular to the direction of the axis of each roller 7and perpendicular to the direction of the movement of each roller 7.FIG. 5 is a view (side view) from the direction of the movement of eachroller 7. FIG. 6 is a view (bottom view) from the direction of the axisof each roller 7. Roller retainers 15 of the same number as that of therollers 7 are provided to retain the rollers 7 individually. Each of theroller retainers 15 is made thin to hold front and rear surfaces of acorresponding roller 7 in the direction of the movement of the roller 7.The frontal shape of the roller retainer 15 (viewed from the directionperpendicular to the axis of the roller and perpendicular to thedirection of the movement of the roller) is formed like a frame. Thethickness W of each side surface of the roller retainer 15 is set to bein a range of from 50% to 90%, preferably in a range of from 50% to 60%of the diameter of the roller. Incidentally, when a tapered roller isused as the roller 7, the diameter of the roller is minimized.

A linear guide portion 16 a and a curve guide portion 16 b different ininclination angle from each other are formed in an end surface 16 of aroller retainer 15 in the direction of the movement of the rollerretainer 15. A linear guide portion 17 a and a curve guide portion 17 bdifferent in inclination angle from each other are formed in the otherend surface 17 of the roller retainer 15 in the direction of themovement of the roller retainer 15. The linear guide portions 16 a and17 a are formed so as to be substantially parallel to the axis of eachroller 7. The curve guide portions 16 b and 17 b are formed so that thecurve guide portions 16 b and 17 b face radial directions respectivelywhen roller retainers are arranged in a curved race. That is, in acurved race, the curve guide portions 16 b and 17 b of the rollerretainer 15 come into contact with adjacent roller retainers 15 and, ina linear race, the linear guide portions 16 a and 17 a of the rollerretainer 15 come into contact with adjacent roller retainers 15. Thelinear guide portions 16 a and 17 a and the curve guide portions 16 band 17 b of the roller retainer 15 are formed to be sectionally circulararc-shaped curved surfaces so as to come into linear contact withadjacent roller retainers 15 (see FIG. 6). As shown in FIG. 5, fourcorners of side surfaces of the roller retainer 15 are cut to bechamfered portions 18. Hence, the roller retainer 15 can be preventedfrom interfering with the screw shaft 5 even in the case where the axis19 of the roller 7 is arranged not to be perpendicular to the centerline 5 c of the screw shaft 5 but to be inclined at an angle a as shownin FIG. 1. As shown in FIG. 4, a pair of drop-down preventionprotrusions 20, 20 are formed on the upper and lower portions, on theroller 7 side, of the roller retainer 15. Further, a pair of recesses21, 21 are formed on the side surface of the roller 7 so that therecesses 21 are fitted to the protrusions 20, 20. Hence, the rollerretainer 15 holds the roller 7 so that the roller 7 can rotate aroundits axis 19. Incidentally, the drop-down prevention protrusions 20 maybe provided on the roller 7 side while the drop-down prevention recesses21 may be provided on the roller retainer 15 side. The roller retainer15 is made from a synthetic resin or the like, as a raw material, byinjection molding, or the like.

A tapered roller can be used as the roller 7. The apex Q of the cone ofthe tapered roller is located on the center line 5 c of the screw shaft5. Hence, the tapered roller rolls without slipping between the loadrolling groove 6 a and the roller rolling groove 5 a. Incidentally, thesectional shape of the roller rolling groove 5 a, the sectional shape ofthe load rolling groove 6 a and the side shape of the roller can be setfreely in accordance with load, accuracy, etc. required of the rollerscrew.

As shown in FIG. 1, when the screw shaft 5 is rotated, rollers 7 androller retainers 15 rolling in the load rolling passage 8 in thedirection of the circumference of the screw shaft 5 while suffering loadare scooped by the return pipe 9. The scooped rollers 7 and rollerretainers 15 pass through the return pipe 9. Then, the rollers 7 androller retainers 15 are returned to the load rolling passage 8 after thedistance of several pitches. When the direction of the rotation of thescrew shaft 5 is inverted, the respective rollers 7 circulate in thereverse course. Incidentally, the nut member 6 may be rotated in thecondition that the screw shaft 5 is provided as a stationary side. Alsoin this case, the rollers 7 can circulate in the aforementioned manner.

FIG. 7 shows rollers 7 and roller retainers 15 circulating in the returnpipe 9 and the load rolling passage 8. As shown in FIG. 7, in a linearrace (in a return pipe 9) constituting a circulation path, a linearguide portion 16 a of a roller retainer 15 located in the rear side inthe direction (1) of the movement of the roller 7 presses a linear guideportion 17 a of another roller retainer 15 located in the front side. Ina curved race (in a load rolling passage 8), the curve guide portion 16b of the rear-side roller retainer 15 presses the curve guide portion 17b of the front-side roller retainer 15. Either in the linear race or inthe curved race, the rear-side roller retainer 15 can press thefront-side roller retainer 15 without spoiling the posture of the roller7 located in the rear side in the direction of the movement of therollers 7. When a tapered roller is used as each of the rollers 7,particularly in a linear race, the roller 7 tries to fall down in aplane containing the axis and the direction of the movement of theroller. In the linear race, linear guide portions 16 a and 17 a ofadjacent roller retainers 15 come into close contact with each other,while, in the curved race, curve guide portions 16 b and 17 b ofadjacent roller retainers 15 come into close contact with each other. Asa result, the rollers 7 are aligned so that smooth circulation can beobtained. In most cases, the return pipe 9 in a no-load region has alinear race, a circular-arc race, a linear race, and a circular-arcrace. When the curvature of a circular arc 24 of the return pipe 9 ismade coincide with the curvature of the load rolling passage 8, rollers7 can be aligned so that smooth circulation can be obtained. This isbecause the curve guide portions 16 b and 17 b of adjacent rollerretainers 15 come into close contact with each other even in thecircular arc portion of the return pipe 9. When the curvature of thecircular arc 24 of the return pipe 9 does not coincide with thecurvature of the load rolling passage 8, the curve guide portions 16 band 17 b may be further separated into two portions different ininclination angle. That is, guide portions may be separated into threestages, for example, a linear guide portion, a curve guide portion forload rolling passage and a curve guide portion for return pipe, may beformed.

As described above, the load rolling passage 8 of the roller screw isformed helically. As described above with reference to FIG. 2, thereturn pipe for changing the direction of the scooped roller 7 has atorsion (torsional angle θ1) around the direction of the movement of theroller. That is, in the roller screw, the rollers 7 and roller retainers15 change their directions three-dimensionally and make complex motion.The aforementioned roller retainers 15 are adapted to such a complexmotion. As shown in FIG. 5, the thickness W of each side of each rollerretainer 15 is made small. Furthermore, the linear guide portions 16 aand 17 a (to be in close-contact) and curve guide portions 16 b and 17 b(to be in close-contact) of adjacent roller retainers 15 are shaped likecircular arcs in section so as to come into linear contact with eachother. Hence, such adjacent roller retainers 15 press each other whilethey are allowed to rotate slightly around the axes of correspondingrollers 7 respectively. As a result, the roller retainers 15 freelychange their direction three-dimensionally with corresponding rollers 7respectively, so that complex motion required of the roller screw inthis embodiment can be made. Particularly when the axis 19 of eachroller 7 is not perpendicular to the center line 5 c of the screw shaft5 but inclined at a predetermined angle as shown in FIG. 1, the roller 7circulates in an umbrella-like curved race. Therefore, adjacent rollerretainers 15 need to come into close contact with each other while acrossing angle β between the adjacent roller retainers 15 is keptconstant as shown in FIG. 8. According to the present invention,adjacent roller retainers 15 press each other while they are allowed torotate slightly around the axes of corresponding rollers 7 respectively.Accordingly, roller retainers 15 sufficiently adapted to suchcirculation form can be obtained.

Because each of the roller retainers 15 is made thin, a large space canbe ensured for reserving lubricating oil in the circulation path. Hence,the rollers 7 can be lubricated sufficiently. Furthermore, because eachof the roller retainers 15 is made thin, a large gap can be takenbetween the roller retainers 15 and the load rolling groove 6 a. Hence,a support member for supporting the roller retainers 15 can be providedin the circulation path to prevent the roller retainers 15 from droppingdown from the nut member 6, or the like.

FIG. 9 shows the case where the thickness of each roller retainer 15 isselected to be smaller than 50% of the roller diameter. If the thicknessof the roller retainer 15 is made smaller than 50% of the rollerdiameter, the front end of the succeeding roller retainer 15 enters thegap between the front-side roller retainer 15 and the roller rollinggroove 5 a so that adjacent roller retainers 15 may overlap each other.As a result, there is a risk that the circulation of the rollers 7 maystop. When the thickness of the roller retainer 15 is selected to be notsmaller than 50% of the roller diameter, adjacent roller retainers 15can be prevented from overlapping each other as described above.

FIG. 10 shows a second embodiment of the present invention concerningrollers and roller retainers incorporated in the roller screw. Each ofthe roller retainers 25 has substantially the same configuration as thatof the roller retainer 15 according to the first embodiment. The rollerretainer 25 further has a hinge protrusion 26, and a hinge recess 27fitted to the hinge protrusion 26 of the adjacent roller retainer 25.The hinge protrusion 26 is provided at a point of intersection betweenthe linear guide portion 16 a and the curve guide portion 16 b on oneend surface of the roller retainer 25 in the direction of the movementof the roller 7. The hinge recess 27 is provided at a point ofintersection between the linear guide portion 17 a and the curve guideportion 17 b on the other end surface of the roller retainer 25. Becausethe hinge protrusion 26 and the hinge recess 27 are provided in theaforementioned manner, the roller retainer 25 is only allowed to swingaround a hinge constituted by a combination of the hinge protrusion 26and the hinge recess 27 in a plane containing the axis of acorresponding roller 7 and the direction (1) of the movement of theroller 7. Hence, the roller 7 can be prevented from falling down even inthe boundary in which the roller is moving from the linear race to thecurved race. Hence, smooth circulation of the roller 7 can be ensured.

FIGS. 11 to 13 and FIGS. 14A to 14C show a third embodiment of thepresent invention concerning roller retainers incorporated in the rollerscrew. FIG. 11 is a view (front view) from a direction perpendicular tothe axis of each roller 7 and perpendicular to the direction (1) of themovement of the roller 7. FIG. 12 is a view (side view) from the rearside in the direction of the movement of the roller 7. FIG. 13 is a view(bottom view) from the direction of the axis of the roller 7. FIGS. 14Ato 14C are views showing the case where roller retainers with rollers 7are aligned in a line. In this embodiment, each of the roller retainers31 is made thin to hold only the opposite side surfaces of acorresponding roller 7 and the front surface of the same roller 7 in thedirection of the movement of the roller 7. Each of the roller retainers31 is shaped like a U figure in front view. The thickness W of each sideof the roller retainer 31 is selected to be in a range of from 50% to90%, preferably in a range of from 50% to 60% of the roller diameter.

A linear guide portion 32 a and a curve guide portion 32 b which aredifferent in inclination angle from each other are formed in one endsurface of the roller retainer 31 in the direction of the movementthereof. The linear guide portion 32 a is inclined at a predeterminedangle with respect to the axis of the roller 7 so that the axes ofadjacent rollers 7 are kept parallel to each other. The curve guideportion 32 b is inclined so that the roller retainers 31 face radialdirections when the roller retainers 31 are arranged in a curved race.That is, in a curved race, the curve guide portion 32 b comes intocontact with an adjacent roller 7 and, in a linear race, the linearguide portion 32 a comes into contact with the adjacent roller 7. Thelinear guide portion 32 a and the curve guide portion 32 b are formed asa curved surface corresponding to the outer circumference of the roller7.

According to this roller retainer 31, the roller retainer 31 and aroller 7 adjacent to the roller retainer 31 can press each other whilethe roller retainer 31 is allowed to rotate slightly around the axis ofa corresponding roller 7 in the same manner as that in the rollerretainer 15 in the first embodiment. Hence, the roller retainer 31 canfulfil the same operation and effect as those of the roller retainer 15obtained in the first embodiment. Furthermore, because the rollerretainer 31 comes into surface contact with a roller 7 located in thefront side or rear side in the direction of the movement of the roller,contact surface pressure can be also reduced.

In the example of this roller screw, rollers 7 rolling in the rollerrolling groove 5 a of the screw shaft 5 are scooped by the return pipe 9and returned by several pitches. Alternatively, a deflector for scoopingrollers 7 may be provided in the nut member 6. That is, one of rollers 7rolling on the roller rolling groove 5 a of the screw shaft 5 may bepicked out from the roller rolling groove 5 a by the deflector so thatthe roller 7 skips over the outer diameter portion of the screw shaft 5and returns to the roller rolling groove 5 a before one lead. Though notshown, a so-called side cover type roller screw may be used. That is,the nut member 6 is constituted by a nut body having a load rollinggroove formed therein and side covers attached to opposite ends of thenut body. A roller return passage is formed in the nut body. Acommunication passage by which the load rolling groove and the returnpassage communicate with each other is formed in each of the sidecovers.

The roller retainer according to the present invention is not limitedonly to the roller screw, but can be applied to a direct-acting guidedevice such as a linear guide or a spline. Particularly the rollerretainer according to the present invention can be adapted to adirect-acting guide device except the case where each roller circulatestwo-dimensionally in a plane perpendicular to the axis of the roller.That is, the roller retainer according to the present invention can beadapted to a direct-acting guide device having a circulation path whichis so complex that the path is bent while the roller is twisted.

FIG. 15 shows a linear guide in which roller retainers 15 according tothe first embodiment of the present invention are incorporated. Thelinear guide is a well known device for guiding a movable body such as atable on a stationary portion such as a bed or a saddle. The linearguide has a guide rail 41 (race shaft), a moving block (slide member)42, and a plurality of rollers 43. The guide rail 41 is disposed on thestationary portion and has a roller rolling groove 41 a which is formedalong the direction of the length thereof so that the roller rollinggroove 41 a serves as a roller rolling surface. The moving block 42 isfitted to the guide rail 41 so as to be relatively movable. A rollercirculation path containing a load rolling groove 42 a corresponding tothe roller rolling grove 41 a of the guide rail 41 is formed in themoving block 42 so that the load rolling groove 42 a serves as a loadrolling surface. The plurality of rollers 43 are arranged and receivedin the roller circulation path and circulate in the roller circulationpath in accordance with the relative movement of the moving block 42 tothe guide rail 41. The plurality of rollers 43 are held in the rollerretainers 15 individually and correspondingly. The rollers 43 arearranged and received in the roller circulation path so that the axes ofthe rollers 43 are substantially kept parallel to one another. With theendless circulation of the rollers 43, the moving block 42 supportingthe rollers makes linear motion along the guide rail 41.

The guide rail 41 is slenderly elongated to form a quadrilateral insection. A roller rolling groove 41 a, which serves as a race when aroller 43 rolls, is formed in each of left and right side surfaces ofthe guide rail 41 so as to extend over the whole length of the guiderail. Although FIG. 15 shows the case where the race rail is linear, theinvention may be applied also to the case where the rail is curved.Although FIG. 15 shows the case where two roller rolling grooves 41 aare provided in left and right, the invention may be applied also to thecase where the number of roller rolling grooves is changed variously inaccordance with the purpose of use of the linear guide, or the like.

The moving block 42 is roughly constituted by a combination of a movingbody 44 and a pair of side covers (not shown) disposed at opposite endsof the moving body 44. Two load rolling grooves 42 a corresponding tothe roller rolling grooves 41 a are provided in the moving body 44. Thecombination of the load rolling grooves 42 a and the roller rollinggrooves 41 a forms two load rolling passages C between the guide rail 41and the moving block 42.

Two return passages D extending in parallel to the load rolling passagesC respectively and changing-direction passages B for connecting the loadrolling passages C to the return passages D respectively are furtherprovided in the moving body 44. The combination of the load rollingpassages C, the return passages D and the pair of changing-directionpassages for connecting the load rolling passages C to the returnpassages D respectively forms one roller circulation path. Each of thechanging-direction passages B has a three-dimensionally complex race.

As the moving block 42 moves along the guide rail 41, the roller 43rolls in the load rolling passage C from one end to the other end whilethe roller 43 suffers load from the moving block 42. Then, each of therollers 43 is scooped by one changing-direction passage B and led to thereturn passage D. The roller 43 is further returned to one end of theload rolling passage C through the opposite changing-direction passageB. On this occasion, in the load rolling passages C and return passagesD constituting a linear race, the linear guide portion of the rear-sideroller retainer 15 presses the linear guide portion of the front-sideroller retainer 15. In the changing-direction passages B constituting acurved race, the curve guide portion of the rear-side roller retainer 15presses the curve guide portion of the front-side roller retainer 15.Either in the linear race or in the curved race, the rear-side rollerretainer 15 can press the front-side roller retainer 15 without spoilingthe posture of the roller 7 located in the front side in the directionof the movement of the rollers.

As described above, each side surface of the roller retainer 15 is madethin, and the linear guide portion and curve guide portion for makingadjacent roller retainers in close contact with each other are shapedlike circular arcs in section so that they come into linear contact withadjacent roller retainers. Hence, adjacent roller retainers press eachother while they are allowed to rotate slightly around the axes ofcorresponding rollers respectively. In such a manner, the rollerretainers 15 with the rollers 43 can change their directionthree-dimensionally freely. Hence, the roller retainers 15 can make suchcomplex motion as that required of the changing-direction passages B ofthe linear guide in this embodiment.

Although this embodiment has shown the case where the relative movementof the moving block 42 to the guide rail 41 is made linearly, thepresent invention may be preferably applied also to a guide device whichis configured so that the relative motion is curved.

FIG. 16 shows a spline in which roller retainers according to the firstembodiment of the present invention are incorporated. The spline has aspline shaft 51, and an outer cylinder 52. The spline shaft 51 serves asa race member whereas the outer cylinder 52 serves as a slide member.The outer cylinder 52 is mounted on the spline shaft 51 so as to bemovable through a plurality of rollers 53. The plurality of rollers 53are held in roller retainers 15, individually, obtained in the firstembodiment. Further, the axes of adjacent rollers are substantially keptparallel to each other.

The spline shaft 51 is shaped like a column of a true circle. Aplurality of roller rolling grooves 51 a, which act as roller races andserve as roller rolling surfaces extending in the axial direction of thespline shaft 51, are formed in a surface of the spline shaft 51. Forexample, six roller rolling grooves 51 a are formed.

The outer cylinder 52 mounted on the spline shaft 51 has load rollinggrooves 52 a corresponding to the roller rolling grooves 51 a. The loadrolling grooves 52 a serve as load rolling surfaces. A plurality ofrollers 53 are arranged in the roller circulation path so that therollers 53 circulate in addition to the linear movement of the outercylinder 52 relative to the spline shaft 51. A load rolling passage C isformed between each load rolling groove 52 a formed in the outercylinder 52 and a corresponding roller rolling groove 51 a formed in thespline shaft 51. Ano-load return passage D is formed adjacently to eachload rolling passage C. In the no-load return passage D, rollers 53,which is released from load, roll. A changing-direction passage B forconnecting each load rolling passage C to a corresponding no-load returnpassage D is further formed in the outer cylinder 52. Thechanging-direction passage B has a three-dimensionally complex race likethat of the linear guide.

When the outer cylinder 52 is moved relatively to the spline shaft 51,the roller 53 rolls in the no-load rolling passage C while it suffersload. Hence the roller 53 changes its direction in thechanging-direction passage B and moves to the no-load return passage D.In the no-load return passage D, the roller 53 moves in the reversedirection against the load rolling passage C. The rollers 53 moving inthe no-load return passage D change its direction again in the otherchanging-direction passage B and return to the no-load return passage Cagain. On this occasion, in the load rolling passages C and no-loadreturn passages D constituting linear races, the linear guide portion ofthe rear-side roller retainer 15 presses the linear guide portion of thefront-side roller retainer 15. In the changing-direction passage Bconstituting curved race, the curve guide portion of the rear-sideroller retainer 15 presses the curve guide portion of the front-sideroller retainer 15. Either in the linear race or in the curved race, therear-side roller retainer 15 can press the front-side roller retainer 15without spoiling the posture of the roller 53 located in the front sidein the direction of the movement of the roller.

Further, each side surface of the roller retainer 15 is made thin, andthe linear guide portion and curve guide portion for making adjacentroller retainers 15 in close contact with each other are shaped likecircular arcs in section so that they come into linear contact withadjacent roller retainers. Hence, adjacent roller retainers 15 presseach other while they are allowed to rotate slightly around the axes ofcorresponding rollers respectively. In such a manner, the rollerretainers 15 with the rollers 53 can change their directionthree-dimensionally freely. Hence, the roller retainers 15 can make suchcomplex motion as that required of the changing-direction passages B ofthe spline in this embodiment.

As described above, according to the present invention, a rollerretainer is made thin to hold opposite side surfaces of a correspondingroller and front and rear surfaces of the roller in the direction of themovement of the roller. A linear guide portion and a curve guide portiondifferent in inclination angle from each other are formed in each endsurface of the roller retainer in the direction of the movement of theroller retainer. Hence, in the curved race, the curve guide portioncomes into contact with an adjacent roller retainer. In the linear race,the linear guide portion comes into contact with an adjacent rollerretainer. Hence, in either of the linear race and curved raceconstituting a circulation race, the rear-side roller retainer can pressthe front-side roller retainer without spoiling the posture of theroller located in the front side in the direction of the movement of theroller. Hence, rollers can be aligned so that smooth circulation can beobtained. Further, because the roller retainer is made thin, thefollowing effects are obtained.

(1) Adjacent roller retainers can press each other while they areallowed to rotate slightly around the axes of corresponding rollersrespectively. As a result, the roller retainer can be obtained as aroller retainer adapted to a complex circulation path such as athree-dimensional changing-direction passage or a helical load rollingpassage shaped like a screw.

(2) A large space can be secured for reserving lubricating oil in thecirculation path. Hence, the rollers can be lubricated sufficiently.

(3) A drop-down prevention member for supporting the roller retainer canbe provided in the circulation path so that the roller retainer isprevented from dropping down from the nut member, or the like.

What is claimed is:
 1. A roller retainer assembly, comprising: aplurality of roller retainers for individually correspondingly retaininga plurality of rollers circulating in a roller circulation pathinclusive of linear and curved races; wherein each of said rollerretainers hold opposite side surfaces of said roller and either one offront and rear surfaces of said roller in a direction of movement ofsaid roller; wherein a linear guide portion and a curve guide portionwhich are different in inclination angle from each other are formed inone end surface of said roller retainer in a direction of movement ofsaid roller retainer; and wherein said linear guide portion of saidroller retainer comes into contact with an adjacent roller in saidlinear race and said curve guide portion of said roller retainer comesinto contact with said adjacent roller in said curved race.
 2. A rollerretainer assembly according to claim 1, wherein each of said linearguide portion and said curve guide portion of said roller retainer isformed to be a curved surface in accordance with an outer circumferenceof said roller.
 3. A roller retainer assembly according to claim 1,wherein the plurality of rollers have a cylindrical or substantiallycylindrical shape.
 4. A direct-acting guide device comprising: a raceshaft containing a roller rolling surface; a slide member including aroller circulation path containing a load rolling surface correspondingto said roller rolling surface, said slide member being fitted to saidrace shaft so as to be freely movable relative to said race shaft; aplurality of rollers arranged and received in said roller circulationpath so as to circulate in accordance with movement of said slide memberrelative to said race shaft; and a plurality of roller retainers forholding said plurality of rollers individually and correspondingly sothat said plurality of rollers are rotatable and/or slidable; whereinsaid plurality of rollers are arranged and received so that axes ofadjacent rollers are kept approximately parallel to each other; whereineach of said roller retainers hold opposite side surfaces ofcorresponding one of said rollers and either one of front and rearsurfaces of said roller in a direction of movement of said roller;wherein a linear guide portion and a curve guide portion which aredifferent in inclination angle from each other are formed in one endsurface of said roller retainer in a direction of movement of saidroller retainer; and wherein said linear guide portion of said rollerretainer comes into contact with an adjacent roller in a linear race andsaid curve guide portion of said roller retainer comes into contact withsaid adjacent roller in a curved race.
 5. A direct-acting guide deviceaccording to claim 4, wherein the plurality of rollers have acylindrical or substantially cylindrical shape.
 6. A roller screwcomprising: a race shaft containing a helical roller rolling surface; aslide member including a roller circulation path containing a helicalload rolling surface corresponding to said roller rolling surface, saidslide member being fitted to said race shaft so as to be freely movablerelative to said race shaft; a plurality of rollers arranged andreceived in said roller circulation path so as to circulate inaccordance with movement of said slide member relative to said raceshaft; and a plurality of roller retainers for holding said plurality ofrollers individually and correspondingly so that said plurality ofrollers are rotatable and/or slidable; wherein said plurality of rollersare arranged and received so that axes of adjacent rollers are keptapproximately parallel to each other; wherein each of said rollerretainers hold opposite side surfaces of corresponding one of saidrollers and either one of front and rear surfaces of said roller in adirection of movement of said roller; wherein a linear guide portion anda curve guide portion which are different in inclination angle from eachother are formed in one end surface of said roller retainer in adirection of movement of said roller retainer; and wherein said linearguide portion of said roller retainer comes into contact with anadjacent roller in a linear race and said curve guide portion of saidroller retainer comes into contact with said adjacent roller in a curvedrace.
 7. A roller screw according to claim 6, wherein the plurality ofrollers have a cylindrical or substantially cylindrical shape.